/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponents/Public/PreviewMesh.h
Enable secondary triangle buffers. The Secondary material will be applied to any triangles that pass TriangleFilterFunc.
void EnableSecondaryTriangleBuffers ( [TUniqueFunction](API\Runtime\Core\Templates\TUniqueFunction)< bool(const [FDynamicMesh3](API\Runtime\GeometryCore\DynamicMesh\FDynamicMesh3) *, int32)> TriangleFilterFunc )